ES2939968T3 - Method for preparing lithium titanate spinel nanoparticles - Google Patents

Abstract

The invention provides a method for preparing lithium-containing particles suitable for use in a battery electrode, the method includes forming a mixture comprising titanium dioxide precursor particles and an aqueous solution of a lithium compound; and heating the mixture at elevated temperature in a sealed pressure vessel to form lithium-embedded titanium dioxide particles, wherein at least one particle size characteristic selected from average primary particle size, particle size distribution, average intraparticle pore size, average particle size between - the pore size of the particles, the pore size distribution and the shape of the titanium dioxide particles do not substantially change in said heating step. The invention also includes a battery that includes a first electrode, a second electrode, (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Method for preparing lithium titanate spinel nanoparticles

FIELD OF THE INVENTION

The present invention is directed to lithium intercalated titanium dioxide particles and lithium titanate particles adapted for use in anodes for lithium ion batteries, as well as methods of forming such particles.

BACKGROUND

Lithium ion batteries are rechargeable batteries that rely on the movement of lithium ions between electrodes. Such batteries are commonly used in a variety of electronic products due to their high energy density, high power density, and fast charge/discharge characteristics. The anode typically consists of graphite and the cathode typically consists of a lithium intercalation material, such as LiCoO ² , the electrodes being connected via a liquid electrolyte, such as LiPF6 in a non-aqueous solvent.

There is a need in the art for improved anode materials for use in lithium ion batteries to replace conventional carbon-based materials, such as graphite, which in some cases can suffer from relatively short life cycles and relatively long charging times. Lithium titanate having a spinel crystal structure (ie Li4Ti5O12 also known as LTO) is increasingly used as anode materials in lithium-ion batteries, especially for electric automobile and energy storage applications. Lithium titanate changes to a rock salt crystal structure as lithium ions are inserted during charging, and changes back to a spinel crystal structure as lithium ions dissociate. Lithium titanate experiences much less change in its lattice volume due to charge/discharge compared to carbon materials, and generates little heat even when shorted to the positive electrode, thus avoiding fire accidents and ensuring a high degree of security. Additionally, the use of lithium titanate as the anode material results in longer battery life (rechargeable for more cycles) and shorter charge time (minutes vs. hours).

It is highly desirable that lithium titanate have a cubic spinel structure with high crystal ordering and phase purity to produce a high level of performance in lithium ion batteries. Lithium titanate spinels, like other ceramic materials, can be prepared by conventional solid-state reaction processes; that is, mixing the oxide components and heating or firing the mixture to facilitate the reaction in the solid state. Due to the kinetic limitations of solid state reagents, it is difficult to achieve a high purity phase with uniform particle size and morphology. Also, lithium can be lost during heating or cooking due to the volatile nature of lithium compounds.

To overcome these limitations, wet chemistry techniques involving one or more lithium or titanium compounds dissolved or suspended in a solvent have been proposed. However, many of these processes have certain disadvantages, such as lack of reaction control, inhomogeneous reactions, and/or the inability to adequately control particle morphology, particle size, or crystallinity. There remains a need in the art for a method of forming lithium titanate spinel particles of controlled particle size and morphology for use in lithium ion battery applications.

Tomiha et al., J. Mater. Sci., 37 (2002), 2341-2344 disclose alkaline titanates A2TinO2n+1 (A=Li, Na, K) synthesized by hydrothermal reaction of titania powder in an aqueous alkaline solution. A nanometer-sized titania powder of 7 nm in diameter was used as a starting material to progress the hydrothermal reaction at 100°C.

DE 10 2008 026580 A1 discloses doped and undoped lithium titanate Li4Ti5O12, obtainable by thermal reaction of a stoichiometric compound oxide containing Li ² TiO ³ and TiO ² , preparation of the stoichiometric compound oxide and a process for the preparation of lithium titanate Li4Ti5O12 and its use as anode material in rechargeable lithium-ion batteries.

SUMMARY OF THE INVENTION

The present invention provides methods for forming lithium-containing particles suitable for use in a lithium ion battery electrode. For example, the present invention can provide high quality lithium titanate particles with advantageously small particle size (eg, nanometer size range), narrow particle size distribution, and high crystallinity. The use of lithium-containing particles prepared in accordance with the invention can result, in certain embodiments, in battery electrodes that provide greater safety with respect to explosions and fires, greater battery life and shorter charging time compared to carbon-based electrodes.

In one aspect, the invention provides a method for preparing lithium-containing particles suitable for use in a battery electrode, comprising:

a) forming a mixture comprising titanium dioxide precursor nanoparticles and an aqueous solution of a lithium compound, wherein the titanium dioxide precursor particles consist of more than 95% anatase phase;

b) heating the mixture to a temperature of at least about 80°C for at least 3 hours in a sealed pressure vessel under autogenous pressure to form lithium-inserted titanium dioxide nanoparticles, wherein at least one characteristic particle size selected from the group consisting of primary particle mean size, intraparticle mean pore size, interparticle mean pore size of the titanium dioxide nanoparticles is within 10 percent of the same characteristic of titanium dioxide precursor nanoparticles; and

c) calcining the lithium-embedded titanium dioxide nanoparticles to form lithium titanate spinel nanoparticles.

At least one of the primary mean particle size, mean intraparticle pore size, and mean interparticle pore size of the lithium-inserted titanium dioxide particles may be within about 5 percent of the same size characteristic. of the titanium dioxide precursor particles. In certain advantageous embodiments, both the titanium dioxide precursor particles and the lithium-inserted titanium dioxide particles are characterized by one or more of the following: a mean primary particle size of less than about 100 nm; a generally spherical shape; a mean intraparticle pore size in the mesopore range; a monodisperse particle size distribution; and a monodisperse intraparticle pore size distribution.

The lithium compound used in the invention can vary, with examples including lithium hydroxide, lithium oxide, lithium chloride, lithium carbonate, lithium acetate, lithium nitrate, and combinations thereof. The elevated temperature is typically at least about 80°C and the pressure during the heating step is typically autogenous. In certain embodiments, the pH of the mixture is greater than about 9. Typically, the pressure applied to the mixture during the heating step is at least about 20 psig. In one embodiment, the amount of lithium compound in the mixture is between about 2 and about 20 percent by weight based on the weight of the titanium dioxide particles.

The method includes calcining the lithium-inserted titanium dioxide particles to form lithium titanate spinel particles (for example, a calcination step comprising heating the lithium-inserted titanium dioxide particles to a temperature of no more than of about 650°C). In certain embodiments, the lithium titanate spinel particles are characterized by one or more of the following: a mean primary particle size of less than about 100 nm; an intraparticle mean pore size in the mesopore range; a monodisperse particle size distribution; and a monodisperse intraparticle pore size distribution. Advantageously, at least one of the mean primary particle size, mean intraparticle pore size, and mean interparticle pore size of the litho titanate spinel particles is within about 10 percent of the same characteristic of Titanium dioxide precursor particle size.

In a further embodiment, the invention provides a method for preparing lithium-containing particles suitable for use in a battery electrode, comprising:

a) preparing titanium dioxide precursor particles by forming an aqueous solution of a titanium salt and an organic acid, and thermally hydrolyzing the aqueous solution at an elevated temperature, optionally in the presence of a titanium dioxide seed material, to produce precursor particles of titanium dioxide in a mother liquor;

b) separating the titanium dioxide precursor particles resulting from the mother liquor;

c) optionally, drying the separated titanium dioxide precursor particles;

d) forming a mixture comprising the titanium dioxide precursor nanoparticles and an aqueous solution of a lithium compound, wherein the titanium dioxide precursor particles consist of more than 95% anatase phase;

e) heating the mixture to a temperature of at least about 80°C for at least about 3 hours in a sealed pressure vessel under autogenous pressure to form lithium-inserted titanium dioxide nanoparticles, wherein at least one Particle size characteristic selected from the group consisting of primary particle mean size, intraparticle mean pore size, interparticle mean pore size of the titanium dioxide nanoparticles is within 10 percent of the same characteristic of the nanoparticles titanium dioxide precursors; and

f) calcining the titanium dioxide particles with lithium insertion to form spinel nanoparticles of lithium titanate.

In another aspect, the invention provides a battery (for example, a lithium ion battery) comprising a first electrode, a second electrode and a separator comprising an electrolyte between the first and second electrodes, wherein one of the first and second electrodes the second electrode comprises lithium titanate spinel particles made according to any of the processes outlined above.

In yet another aspect, a battery (eg, a lithium ion battery) is disclosed comprising a first electrode, a second electrode and a separator comprising an electrolyte between the first and second electrodes, wherein one of the first and second electrodes the second electrode comprises titanium dioxide particles with lithium insert. The titanium dioxide particles with lithium insert are according to claim 6.

In a still further aspect, the disclosure provides lithium-inlaid titanium dioxide nanoparticles comprising between about 1 and about 12 weight percent lithium, based on the total weight of the lithium-inlaid titanium dioxide nanoparticles. lithium. In accordance with the invention, lithium-embedded titanium dioxide nanoparticles are characterized by a generally spherical shape and a monodisperse particle size distribution, wherein the nanoparticles have a mean primary particle size of no more than about 80 nm. and a particle size monodispersity such that all particles have a primary particle size within about 10 percent of the mean primary particle size.

Furthermore, the invention provides lithium titanate spinel nanoparticles characterized by one or more of the following: an intraparticle mean pore size in the mesopore range; a monodisperse particle size distribution; and a monodisperse intraparticle pore size distribution. Lithium titanate spinel nanoparticles have a mean particle size of no more than about 80 nm and a particle size monodispersity such that all particles have a primary particle size within about 10 percent of the mean particle size. primary particle. Such lithium titanate spinel nanoparticles can be used in a battery (eg, a lithium ion battery) comprising a first electrode, a second electrode and a separator comprising an electrolyte between the first and second electrodes.

These and other features, aspects, and advantages of the disclosure will become apparent upon reading the following detailed description in conjunction with the accompanying drawings, which are briefly described below. The invention includes any combination of two, three, four, or more of the embodiments noted above, as well as combinations of any two, three, four, or more features or elements set forth in this disclosure, regardless of whether such features or elements are expressly combined in a specific embodiment description herein. This disclosure is intended to be read holistically, such that any separable features or elements of the disclosed invention, in any of its various aspects and embodiments, should be viewed as intended to be combinable unless the context clearly indicates otherwise. .

BRIEF DESCRIPTION OF THE DRAWINGS

Having therefore described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and in which:

The FIG. 1 is an SEM image of titanium dioxide precursor nanoparticles according to one embodiment of the invention;

The FIG. 2 is an SEM image of lithium-embedded titanium dioxide nanoparticles in accordance with one embodiment of the invention;

The FIG. 3 is an SEM image of lithium titanate nanoparticles in accordance with one embodiment of the invention;

FIGS. 4A and 4B are TEM images, at different magnifications, of lithium titanate nanoparticles according to one embodiment of the invention;

The FIG. 5 is an X-ray diffraction (XRD) pattern for titanium dioxide precursor nanoparticles according to one embodiment of the invention, with standard anatase titanium dioxide pattern bars as reference;

The FIG. 6 is an XRD pattern for lithium-inserted titanium dioxide nanoparticles according to one embodiment of the invention, with standard anatase titanium dioxide pattern bars as reference;

The FIG. 7 is an XRD pattern for lithium titanate nanoparticles according to one embodiment of the invention, with standard lithium titanate spinel pattern bars as reference; and

The FIG. 8 is a schematic view of an exemplary lithium ion battery in which the lithium-embedded titanium dioxide nanoparticles or lithium titanate nanoparticles of the invention could be used as part of an electrode material.

DETAILED DESCRIPTION OF THE INVENTION

In the following, the invention will be described in more detail with reference to various embodiments. These embodiments are provided to make this disclosure exhaustive and complete, and to fully convey the scope of the invention to those skilled in the art. In fact, the invention can be embodied in many different ways and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Throughout the document like numbers refer to like elements. As used in the specification and appended claims, the singular forms "a", "an", "the", include plural referents unless the context clearly indicates otherwise.

I. Titanium Dioxide Precursor Particles

The titanium dioxide (TiO ² ) precursor particles used in the invention may vary and, in particular, the particle size, particle morphology, crystalline polymorph, crystallite size, pore size and the like may vary. in certain embodiments of the invention. The precursor particles can be characterized as having a fully or substantially pure anatase crystal structure. TiO ² precursor particles consist of more than 95% anatase phase.

For use in electrode applications, ultrafine particles having a narrow particle size distribution are typically preferred. Therefore, the TiO ² precursor particles used in the present invention are ultrafine or nanoparticles. As used herein, the terms "ultrafine particles" or "nanoparticles" refer to particles with at least one dimension less than 100 nm. The ultrafine particles used in the invention will typically have a mean primary particle size of no more than about 100 nm, more often no more than about 80 nm, and in some embodiments no more than about 50 nm, as determined by visual examination. a micrograph. of a transmission electron microscopy ("TEM") image or a scanning electron microscopy ("SEM") image, measuring the diameter of the particles in the image and calculating the mean primary particle size of the measured particles based on to magnification of the TEM or SEM image. The primary particle size of a particle refers to the smallest diameter sphere that completely encloses the particle. The size ranges indicated above are mean values for particles having a distribution of sizes.

In certain embodiments, TiO ² precursor particles can be characterized in terms of particle size distribution. In certain embodiments, the particles can be viewed as monodisperse, meaning that the population of particles is highly uniform in particle size. Certain populations of monodisperse particles useful in the present invention may be characterized as consisting of particles having a primary particle size within 20 percent of the mean primary particle size for the population of particles, or within 15 percent, or within the 10 percent (ie, all particles in the population have a primary particle size within the given percentage range around the mean primary particle size). In an exemplary embodiment, the mean primary particle size is about 50 nm and all particles in the population have a primary particle size in the range of about 40 to about 60 nm (i.e., within 20 percent of the size). primary particle medium).

Other particle size ranges could be used without departing from the present invention, such as microparticles having at least one dimension less than 1000 µm (eg, from about 50 µm to about 1000 µm). It is also possible to use mixtures of particles having different mean particle sizes within the ranges indicated herein (eg, bimodal particle distributions).

The particle morphology (ie, shape) of the TiO ² precursor particles may also vary without departing from the invention. In certain embodiments, the precursor particles will have a generally spherical shape. It is preferred that the precursor particles show a highly uniform particle morphology, which means that there is relatively little variation in particle shape within the particle population.

TiO ² particles suitable for use in the present invention may also be characterized by variable crystallite sizes, with an advantageous size range being less than about 20 nm, such as less than about 15 nm, or less than about 12 nm (for example, from about 4 nm to about 12 nm).

Precursor particles can also be characterized by variable pore size distributions, both in terms of intraparticle and interparticle pores, as well as variable surface area. Exemplary intraparticle pore sizes include mean pore sizes in the mesopore size range, such as from about 2 nm to about 12 nm, and exemplary interparticle pore sizes include mean pore size ranges from about 15 nm to about 80nm. The area of Exemplary average BET surface area of precursor particles used in the invention includes from about 50 m2/g to about 400 m2/g (eg, from about 100 to about 300 m2/g or from about 120 to about 250 m2/g). As will be understood by one skilled in the art, BET specific surface area refers to a specific surface area determined by nitrogen adsorption in accordance with ASTMD 3663-78 standard based on the Brunauer-Emmett-Teller method described in the journal " The Journal of the American Chemical Society", 60, 309 (1938). Pore size measurements can also be made using the BET methodology.

In certain embodiments, TiO ² precursor particles can be characterized in terms of pore size distribution. In certain embodiments, the particles can be viewed as monodisperse in terms of pore size, which means that the population of particles is highly uniform in pore size. Certain populations of monodisperse particles useful in the present invention may be characterized as consisting of particles having a pore size within 20 percent of the mean intraparticle pore size (or interparticle pore size) for the population of particles, or within the 15 percent, or within 10 percent (ie, all particles in the population have a pore size within the given percentage range around the mean pore size). In an exemplary embodiment, the average intraparticle pore size is about 10 nm and all particles in the population have a particle size in the range of about 8 to about 12 nm (i.e., within 20 percent of the median size). of pore).

Suitable TiO ² precursor particles that can be used in the present invention are commercially available from Cristal Global, as the products available under the trade names Tiona® ATI and CristalACTiV™. Reference is also made to the TiO ² particles and manufacturing methods described in US Patent No. 4,012,338 to Urwin; US Patent Publication No. 2005/0175525 to Fu et al.; 2009/0062111 by Fu et al.; and 2009/0324472 by Fu et al.

In one embodiment, the TiO ² precursor particles are provided as described in US Patent Publication No. 2013/0122298 to Fu et al. As generally described therein, TiO ² nanoparticles can be provided by first preparing an aqueous solution of a titanium salt and an organic acid, which functions as a morphology control agent. TiO ² nanoparticles are formed by thermally hydrolyzing the titanium salt solution at a temperature of around 100°C for a few hours. The nanoparticles can be separated from the mother liquor and used as a precursor material for the lithium insert without first drying the particles. Alternatively, the particles could be dried as described in the aforementioned publication before the lithium insertion step. Example 1 below prepares TiO ² nanoparticles according to this general process.

II. Titanium dioxide nanoparticles with lithium insert

The lithium-embedded titanium dioxide nanoparticles are formed through a treatment process applied to the TiO ² precursor particles described above. As used herein, the reference to "lithium-inserted" or "lithium-intercalated" particles refers to particles having lithium ions inserted into the crystal structure of the particle. In the process of the invention, the particle size and morphology of the precursor particles are advantageously maintained, which means that the process through which lithium is introduced does not significantly affect the size and morphology of the particles, providing This gives you more control over these important particle characteristics. Once precursor particles having the desired size and morphological characteristics are formed, the present invention allows for the formation of lithium-containing particles that essentially mimic the original particles in terms of size and shape.

The lithium embedding process involves the hydrothermal treatment of TiO ² particles in the presence of an aqueous solution of a lithium compound. The aqueous solvent is preferably pure water (eg, deionized water), although mixtures of water may be used as the predominant solvent (eg, greater than 50% of the total weight of solvent, more typically greater than 75% or greater than 95%). with other polar cosolvents such as alcohols without departing from the invention. The amount of water used in the mixture is not particularly limited, although it is advantageous to use enough water to keep the lithium compound in dissolved form.

Any lithium compound that is generally soluble and dissociable in water can be used in the solution. Examples of lithium salts include lithium hydroxide, lithium oxide, lithium chloride, lithium carbonate, lithium acetate, lithium nitrate, and the like. Strongly alkaline lithium compounds such as lithium hydroxide are preferred. Less alkaline lithium compounds are typically used in combination with a strong base (for example, sodium hydroxide or ammonia) to raise the pH of the solution. The pH of the reaction mixture is typically greater than about 9, at best greater than about 10.

The mixture of the aqueous solution of the lithium compound and the TiO ² precursor particles is heat treated at elevated temperature under hydrothermal process conditions. The heating step is carried out carried out in a sealed pressure vessel (for example, an autoclave) in such a way that the process can continue at elevated temperature and autogenous pressure. Exemplary autoclave kit useful in the present invention is available from Berghof/America Inc and Parr Instrument Co., and is described in US Patent No. 4,882,128 to Hukvari et al. The operation of such exemplary containers will be apparent to one skilled in the art.

The temperature applied to the mixture during hydrothermal treatment is at least about 80°C, at least about 90°C, at least about 100°C, or at least about 110°C. The temperature will typically not exceed from about 160°C, and in some cases will not exceed about 150°C. A typical temperature range is from about 80°C to about 150°C (eg, from about 100°C to about 130°C). As stated above, the pressure during the hydrothermal process is autogenous, which means that the pressure within the sealed chamber is not controlled externally, but simply results from the heat treatment applied to the chamber. A typical pressure range for the hydrothermal process is from about 5 to about 200 psig (1 psig = 0.108 MPa).

A more typical pressure range is from about 30 to about 120 psig. In certain embodiments, the pressure applied to the mixture can be characterized as at least about 20 psig, at least about 30 psig, or at least about 40 psig. The elevated pressure experienced by the reaction mixture is important in achieving the desired levels of lithium charging within the particles.

The amount of time in which the hydrothermal treatment is applied to the mixture is at least 3 hours. The maximum treatment period is not particularly limited, although treatment beyond about 48 hours is typically not necessary.

The amount of lithium compound used in the mixture will vary and depends in part on the desired level of lithium loading within the particles. The amount of lithium that can be inserted into the precursor particles can vary significantly, with a typical range being from about 1 to about 12 weight percent lithium, based on the total weight of the lithium-inserted particles. A more typical range of lithium insertion is from about 3% to about 8%. If it is desired to calcinate the lithium-inserted particles to form LTO as described in more detail below, the lithium loading of the particles should be in the range of about 5 to about 7 weight percent. The amount of lithium compound used in the mixture to achieve a desired lithium charge level is typically from about 2% to about 20% by weight of lithium versus weight of titanium dioxide.

As noted above, the hydrothermal process used to insert lithium into the precursor particles leaves the size and morphology of the original particles largely intact. Thus, the lithium-inserted particles can be characterized as having essentially the same particle size and morphology characteristics noted above with respect to the precursor particles. For example, the characteristics of the mean particle size, the particle size distribution (for example, monodispersity), the intraparticle and interparticle pore size, the pore size distribution (for example, monodispersity), and the shape of the particle. particle will not be greatly changed by the hydrothermal process. In certain embodiments, any or all of the characteristics listed above can be viewed as relatively unchanged, meaning one or more of the mean particle size, the particle size distribution (e.g., monodispersity), intraparticle and interparticle pore size. , pore size distribution (eg, monodispersity), and particle shape of the lithium-embedded particles will be within about 10 percent (eg, within about 5% or within about 2.5 %) of the value of the same characteristic of the precursor particles.

The lithium-embedded titanium dioxide nanoparticles can be characterized by an X-ray diffraction (XRD) pattern that is distinct from the titanium dioxide precursor nanoparticles, clearly showing that the process of the invention results in diffusion. lithium in the crystalline structure of TiO ² . In one embodiment, the lithium-embedded titanium dioxide nanoparticles are characterized by an XRD diffraction pattern substantially as shown in FIG. 6. As shown, the lithium-embedded titanium dioxide nanoparticles of the invention will typically display an XRD pattern that has peaks at one or more of the following 2-theta diffraction angles: between about 39° and about 40° (eg, at about 39.5°), between about 45° and about 47° (eg, at about 46°), and at about 81°.

One skilled in the art will understand that the diffraction pattern data should not be interpreted as absolute and, therefore, the lithium-inserted titanium dioxide nanoparticles of the invention are not limited to particles having an identical XRD pattern to that of the diffraction pattern. FIG. 6. Any lithium-embedded titanium dioxide nanoparticle having an XRD pattern substantially the same as that of FIG. 6 will be within the scope of the invention. One skilled in the X-ray powder diffraction art can judge the substantial identity of the X-ray powder diffraction patterns. In general, a measurement error of a diffraction angle in an X-ray powder diffractogram is approximately 2 theta = 0.5° or less (more suitably, approximately 2 theta = 0.2° or less) and such a degree This measurement error must be taken into account when considering the X-ray powder diffraction pattern in FIG. 6 or the peak values given above. In other words, the peaks of FIG. 6 and the peak values given above can be seen, in certain embodiments, as /-0.5° or /-0.2°. See Fundamentals of Powder Diffraction and Structural Characterization, Pecharsky and Zavalij, Kluwer Academic Publishers, 2003.

III. Lithium Titanate Nanoparticles

Although the lithium-intercalated nanoparticles prepared according to the above process can be used without further modification as electrode material, in the claimed process, the lithium-intercalated nanoparticles are further processed to form lithium titanate (LTO) particles. Conversion to LTO involves calcining the lithium-intercalated nanoparticles at elevated temperature, such as a temperature from about 400°C to about 800°C. In certain embodiments, the calcination temperature can be characterized as less than about 650°C, less than about 600°C or less than about 550°C. Calcination conditions are typically applied for at least 1 hour or at least 2 hours (eg, 2 to 8 hours). The maximum treatment period is not particularly limited, although treatment beyond about 12 hours is typically not necessary.

The calcination process leaves the original particle size and morphology of the lithium-embedded nanoparticles largely unchanged, although the particles will have a more cubic shape consistent with LTO's cubic spinel structure. Thus, the LTO particles can be characterized as having essentially the same particle size and morphology characteristics noted above with respect to the lithium insert and precursor particles. For example, the characteristics of mean particle size, particle size distribution (eg, monodispersity), intraparticle and interparticle pore size, and pore size distribution (eg, monodispersity) will not change greatly. by the calcination process. In certain embodiments, any or all of the aforementioned characteristics can be viewed as relatively unchanged, meaning that one or more of the mean particle size, particle size distribution (e.g., monodispersity), intraparticle and interparticle pore size and pore size distribution (eg, monodispersity) of the LTO particles will be within about 10 percent (eg, within about 5% or within about 2.5%) of the value thereof characteristic of the precursor particles and/or the particles with lithium insert. IV. battery apps

Generally speaking, lithium-embedded nanoparticles and LTO nanoparticles are ionic conductors and can therefore find use in any application that makes use of materials having ionic conductivity. LTO nanoparticles can be used as electrode materials in lithium-ion batteries. For example, such materials can be used as part of a battery 100 as schematically represented in FIG. 8, although the drawing is exemplary only and is not intended to limit the scope of the invention to a specific lithium ion battery configuration. Battery 100 includes an anode 102, a cathode 104 , and a separator 106 containing electrolyte. Exemplary lithium ion batteries that could be adapted for use with the present invention are set forth, for example, in United States Patent Publication Nos. 2013/0343983 by Ito et al. and 2013/0337302 to Inagaki et al.

In certain embodiments, the LTO nanoparticles of the invention are used in the anode of a lithium ion battery. The anode material for the battery can further include additives such as conductive agents to adjust the conductivity of the anode (eg, graphite, carbon black, or metal powders) and binders or fillers (eg, polysaccharides, thermoplastic resins, or elastic polymers). The materials used in the cathode can vary, and examples include lithium manganate, lithium cobaltate, lithium nickelate, vanadium pentoxides, and the like. The electrolyte is typically made up of a lithium salt and a solvent. Exemplary solvents include propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, y-butyrolactone, methyl formate, methyl acetate, tetrahydrofuran, dimethyl sulfoxide, formamide, dioxolane, and acetonitrile. Exemplary lithium salts include LiPF6, LiClO4, LiCF3SO3, LiN(CF3SO2)2, and LiBF4.

It is noted that the LTO nanoparticles of the invention could also be used as a cathode matrix material in certain battery embodiments, such as lithium-sulfur (Li-S) batteries where the cathode matrix material is intercalated with sulfur.

Aspects of the present invention are more fully illustrated by the following examples, which are set forth to illustrate certain aspects of the present invention and are not construed as limiting thereof.

EXAMPLES

Example 1. Preparation of TiO? with lithium insert

In a heated reactor equipped with a glass condenser and overhead stirrer, 1.195 g deionized water, 79 g hydrochloric acid (37% Fisher Scientific), 7.9 g citric acid monohydrate (Alfa Aesar) and 398 g were mixed. g of titanium oxychloride solution. While constantly stirring, the mixture was heated to 75°C and a small amount of anatase TiO? (0.1% vs. TiO[gamma]; anatase seeds were produced by Cristal). The reaction was held at 75°C for 2 hours. During this period, TiO ² particles begin to form through the hydrolysis of titanium oxychloride. Then the reaction temperature was increased to 85°C and it was maintained for 3 hours at that temperature. The hydrolysis was essentially complete at this stage.

The reaction mixture was cooled to room temperature and stirring was stopped. The TiO ² slurry formed was allowed to settle for approximately 3 hours. Thereafter, with essentially all of the particles settled to the bottom of the vessel, the mother liquor was removed and approximately the same amount of deionized water was added. A small sample was taken and examined under SEM. The SEM image shows that the TiO ² particles are uniform, generally spherical in shape and approximately 40 nm in size, essentially the same as those shown in FIG. 1. A small oven-dried sample was measured by XRD, which showed that the Ti ² was in the anatase form (as shown in FIG. 5). XRD measurements can be made with a PANalytical X'Pert Pro diffractometer using Cu ^{K a 1} radiation of ^Á = 1.540 Á. The diffractometer was equipped with a sealed Cu X-ray tube and an X-Celerator position sensitive detector. Instrument conditions were set at 45 kV, 40 mA, 0.016°20/step, and 50 second dwell time.

After sampling, stirring was restarted and 78.8 g lithium hydroxide monohydrate (Alfa Aesar) was added in small portions. After stirring for approximately 15 minutes, the mixture was transferred to a hydrothermal reactor (Parr Instruments) and treated at 120°C under autogenous pressure for 24 hours. The reaction was then cooled to room temperature and the product was filtered off and washed with deionized water several times until the conductivity of the filtrate was less than 500 gS/cm. The washed sample was dried in an oven at 90°C. SEM measurement showed that the particles were still in the form of fairly uniform nanospheres (as shown in FIG. 2). In comparison with the SEM image (eg, FIG. 1) of the precursor nanoparticles used for insertion, it can be concluded that the nanoparticles remain intact after insertion and that the morphology of the particles has not changed during the treatment. The XRD measurement showed that the TiO ² was still in the anatase form, although with most of the peaks significantly shifted (as shown in FIG. 6). Lithium analysis, using ICP-OES (inductively coupled plasma-optical emission spectrometry) analysis (Thermo Scientific iCAP 6000), showed that the product contained approximately 6 wt% Li, evidencing that the maximum change in XRD was caused by the insertion of lithium into the TiO ² crystal lattices. The TiO ² sample with lithium insert was first dissolved in a hydrofluoric acid solution before measurement. Lithium standard solutions were purchased from High-Purity Standards, Inc.

Example 2. Conversion of TiO ² with lithium insertion to lithium titanate (LTO) spinel

The lithium-embedded TiO ² nanospheres of Example 1 were treated in an oven at 600°C for 6 hours. The SEM image showed that the nanoparticles after conversion were still largely spherical and the original morphological characteristics were largely maintained (as shown in FIG. 3). High magnification TEM images showed that the nanoparticles were cube-shaped in accordance with the cubic spinel structure (as shown in FIGS. 4A and 4B). The XRD pattern of the nanoparticles (shown in FIG. 7) fully matched that of the standard cubic spinel lithium titanate (Li4TisO12).

Many modifications and other embodiments of the invention will occur to one skilled in the art to which this invention relates having the benefit of the teachings presented in the above descriptions and associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and modifications and other embodiments are intended to be included within the scope of the appended claims.

Claims (7)

1. A method of preparing lithium-containing particles suitable for use in a battery electrode, comprising: a) forming a mixture comprising titanium dioxide precursor nanoparticles and an aqueous solution of a lithium compound, wherein the titanium dioxide precursor particles consist of more than 95% anatase phase; b) heating the mixture at a temperature of at least 80°C for at least 3 hours in a sealed pressure vessel under autogenous pressure to form lithium-inserted titanium dioxide nanoparticles, wherein at least one characteristic of The particle size selected from the group consisting of the mean primary particle size, mean intraparticle pore size, mean interparticle pore size, of the titanium dioxide nanoparticles is within 10 percent of the same size characteristic of the titanium dioxide nanoparticles. titanium dioxide precursor nanoparticles; and c) calcining the lithium-embedded titanium dioxide nanoparticles to form lithium titanate spinel nanoparticles. The method of claim 1, wherein both the titanium dioxide precursor particles and the lithium-inserted titanium dioxide particles are characterized by one or more of the following: to. an intraparticle mean pore size in the mesopore range; and b. a monodisperse intraparticle pore size distribution. The method of any one of claims 1 to 2, wherein the lithium compound is selected from the group consisting of lithium hydroxide, lithium oxide, lithium chloride, lithium carbonate, lithium acetate, lithium nitrate, and combinations thereof. The method of any one of claims 1 to 2, wherein the pH of the mixture is greater than about 9, or wherein the amount of lithium compound in the mixture is between 2 and 20 percent by weight on a based on the weight of the titanium dioxide particles. The method of claim 1, wherein the calcining step comprises heating the lithium-embedded titanium dioxide particles to a temperature of not more than 650°C. 6. Lithium-containing particles suitable for use in an electrode of a lithium ion battery, comprising a plurality of lithium titanate spinel nanoparticles, wherein the lithium titanate spinel particles have a mean particle size primary particle size of not more than 80 nm and a particle size monodispersity such that all particles have a primary particle size within 10 percent of the mean primary particle size, optionally wherein said particles are characterized by one or more of the following: Yo. an intraparticle mean pore size in the mesopore range; and ii. a monodisperse intraparticle pore size distribution. A battery comprising a first electrode, a second electrode and a separator comprising an electrolyte between the first and second electrodes, wherein one of the first and second electrodes comprises the particles of claim 6.